This invention is directed to operational amplifier circuitry comprised of insulated gate type field effect transistors, and in particular, to forming an operational amplifier circuit that is characterized by each of the active elements being formed of insulated gate type field effect transistors coupled in complementary pairs.
Digital circuitry comprised entirely of insulated gate field effect transistors, also known as MOS transistors, are well known in the art. Such digital circuitry is usually entirely formed of pairs of complementary coupled P-channel and N-channel transistors, often referred to as perfect complementary coupled MOS transistors or "PC-MOS transistors". When only a P-channel or N-channel transistor is required, in the integrated circuitry, such use is designated as a quasi-C-MOS transistor or "QC-MOS transistor".
It is noted that whereas digital circuitry formed of PC-MOS transistors and QC-MOS transistors have been provided, these MOS transistor constructions have not been utilized to a great degree in forming analog circuitry. Nevertheless, certain characteristics of PC-MOS circuitry, that cause same to be particularly suited for digital operation, are likely to cause same to be equally suited for analog circuit operation. For example, PC-MOS transistors, when utilized in digital circuitry, are utilized in a off-logic mode and, accordingly, current consumption is only effected when the transistor is in a transient state. Since the switching levels of MOS transistors are determined by the threshold voltage, PC-MOS circuits are characterized by one of the MOS transistors of the pair being turned ON when the other MOS transistor of the pair is turned OFF. This complementary operation causes PC-MOS circuits to be very stable, to have an extremely large OFF impedance that permits the magnitude of the logic signals to approach the supply voltage and, additionally, to limit the biasing current to 10.sup.-12 A. Accordingly, such a high input impedance, renders same ideal for use in an operational amplifier circuit capable of operating in an analog mode. It is desired to form each of the active elements of an operational amplifier circuit of PC-MOS and/or QC-MOS transistors so that the operational amplifier can be formed on the same chip as digital circuitry comprised of the same MOS elements.
It is an object of the instant invention to provide an operational amplifier wherein each of the active elements is an insulating-gate-type field effect transistor.
A further object of the instant invention is to provide an operational amplifier for performing a predetermined transfer function that is formed of mirror pairs of C-MOS transistors.
Another object of the instant invention is to monolithically integrate operational amplifier circuitry capable of operating in an analog mode into the same circuit substrate as circuitry adapted to operate in a digital mode.
Still another object of the instant invention is to provide analog circuitry comprised essentially of insulated gate type field effect transistors in order to permit the analog circuitry to be fabricated on a circuit chip with the same reduction in cost, facility and reliability heretofore obtained in digital circuitry comprised of MOS transistors.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.